The present invention provides high molecular weight copolyesters exhibiting improved oxygen and carbon dioxide barrier properties, and little or no acetaldehyde is produced during manufacturing or processing. The invention provides copolyesters having better oxygen and carbon dioxide barrier properties than poly(ethylene terephthalate) which is used universally for food packaging, carbonated soft drink bottles and the packaging applications which require good oxygen and carbon dioxide barrier properties. Poly(ethylene terephthalate) can undergo degradation during preparation and conversion into film, bottles and other packaging materials with the evolution of acetaldehyde. Ultimately, the acetaldehyde becomes entrained in the polyester. The products made therefrom can be adversely affected by the taste of the packaged food or beverage as it diffuses from the material into the food. The polyesters disclosed herein do not generate acetaldehyde and show barrier properties equal to or superior to poly(ethylene terephthalate). These polymers with better oxygen and carbon dioxide barrier properties should fill needs that require better barrier properties than can be provided with poly(ethylene terephthalate).
Copolyester of poly(1,4-cyclohexylenedimethylene terephthalate) having cis and trans isomers of 1,4-cyclohexanedimethanol were disclosed by Kibler, Bell and Smith in U.S. Pat. No. 2,901,466 in 1959. Numerous patents exist wherein poly(ethylene 2,6 napthalene-dicarboxylate) is tauted as having excellent oxygen and carbon dioxide barrier properties. I am unaware of any disclosure of a copolyester having good oxygen and carbon dioxide barrier properties wherein the copolyester is made up of repeat units from naphthalene dicarboxylic acid, terephthalic acid, and high cis isomer content 1,4-cyclohexanedimethanol.